As simple a thing as it may seem, the perfect outdoor plate does not exist. But the Guyot Designs Squishy Bowl and Cup come really close. I've seen these for several years in the Mountain Equipment Coop catalog, but every time I happened to be in the store, they would always be out of them... I finally broke down not that long ago and purchased a set in blue:
Made of food grade silicone, the bowl (with an approximate volume of 600ml, or a little more than 2 cups) and the cup (with an approximate volume of 275ml, or a little more than 1 cup) are both very flexible and easy to use, as it is easy to create a proper spout on either one, to control the flow of liquids more accurately than you've ever had it using a rigid plate.
Additionally, the silicone material these are made from also provides some thermal protection, helping you avoid burned fingers (and lips!!!).
If you've been looking for a dining set for backpacking or travel, you can stop your search! This is the set for you! And as an added bonus, they pack pretty easily, as you can collapse them to fit in pretty much any nook and cranny in your pack! Great design!